The method relates to the coupling of bus systems via multiplex links.
Devices for linking bus systems over relatively long distances are called bus couplers. Coupling via glass-fiber links is of major importance, in particular. In this case, two bus couplers are linked to one another by a connecting path, in this case a glass-fiber line. Each bus coupler converts the signals on its bus system and transmits them via the connecting path to the other bus coupler, which acts on the bus accordingly. A bus system uses data and control lines, the data lines having valid values at times determined by the control lines. A simple bus coupler continuously monitors the control lines and, in the event of a change, transmits both the status of the data lines and the changed status of the control lines. In this case, the data transmission rate required on the glass-fiber link is governed by the number of bits and the speed, which is prescribed by the bus protocol. For example, 8 data bits, 1 parity bit and the status of 9 control lines have to be transmitted for the coupling of SCSI bus systems in accordance with ANSI X3.131. Parallel-serial converters having a length of 10 bits are suitable for this purpose. Since two changes of the control line ACK and REQ are required for the transmission of one byte, four bit packets of 10 bits are transmitted. A maximum rate of 5 Mbyte/s on the bus produces a data rate of at least 200 Mbit/s, corresponding to a signal frequency of 100 MHz on the serial link. The required bandwidth is further increased by clock information. However, the data rate of 5 Mbyte/s on the bus corresponds only to a data rate of 50 Mbit/s on the serial line, only a quarter of which can thus be utilized.